In some wireless communication systems such as orthogonal frequency division multiplexing (OFDM) systems, data is transmitted and received via multiple carrier frequencies. For example, in UWB systems such as MultiBand OFDM Alliance (MBOA) or 802.15.3a systems, there are approximately 128 independent OFDM sub-carriers (tones) that occupy approximately 528 megahertz of bandwidth. Data is modulated and transmitted via many of the sub-carriers. Approximately 10 of the sub-carriers do not necessarily carry information. These sub-carriers, also referred to as pilot tones, may be used to guard the information carrying sub-carriers, to simplify the filtering requirements of the system, or to provide reference phase/amplitude information for the demodulator. The positions of the pilot tones may be defined according to the communication standard or defined by the user/designer of the system. Some pilot tones are located on two ends of the frequency spectrum and some of the pilot tones are interspersed within the frequency spectrum.
Transmission schemes are typically subject to Federal Communications Commission (FCC)'s regulatory requirements, which place restrictions on various aspects of transmission such as bandwidth, power, etc. In current standards proposal for UWB systems, all the sub-carriers, including the pilot tones, are transmitted with approximately the same average power. Since the total amount of power that can be transmitted over the allotted bandwidth is typically restricted for UWB systems, it would be useful if the power could be more efficiently utilized to improve the systems' signal quality. It would also be desirable to achieve the improvements without breaching the regulatory requirements.